1. Field of the Invention
This invention relates to an optical unit and an optical system using the same, and particularly is suitable for a video camera or a still video camera and a copying apparatus or the like utilizing an optical unit comprising a plurality of reflecting surfaces each having a curvature constructed integrally with one another.
2. Related Background Art
There have heretofore been proposed various photographing optical systems utilizing the reflecting surface of a concave mirror, a convex mirror or the like. FIG. 6 of the accompanying drawings is a schematic view of the essential portions of a so-called mirror optical system (reflecting optical system) comprising a concave mirror and a convex mirror.
In the mirror optical system of FIG. 6, an object light beam 124 from an object is reflected by a concave mirror 121 and travels toward the object side while being converged, and is reflected by a convex mirror 122, whereafter it is imaged on an image plane 123.
This mirror optical system is based on the construction of a so-called Cassegrainian reflector, and is directed to shorten the full length of the optical system by bending the optical path of a telephoto lens system of a great full lens length comprised of a refracting lens by the use of two reflecting mirrors opposed to each other.
Also in an objective lens system constituting a telescope, for a similar reason, there are known a number of systems for shortening the full length of the optical system by the use of a plurality of reflecting mirrors, besides the Cassegrainian type.
As described above, by using a reflecting mirror instead of the lens of a photo-taking lens of a great full lens length, the optical path is efficiently bent to thereby provide a compact mirror optical system.
Generally, however, in a mirror optical system such as a Cassegrainian reflector, there is the problem that a part of the object ray of light is eclipsed by the convex mirror 122. This problem is attributable to the fact that the convex mirror 122 is present in the passage area of the object light beam 124.
In order to solve this problem, there has also been proposed a mirror optical system in which a reflecting mirror is made eccentric and used to avoid the other portion of the optical system shielding the passage area of the object light beam 124, i.e., separate the principal ray 126 of the light beam from an optical axis 125.
FIG. 7 of the accompanying drawings is a schematic view of the essential portions of a mirror optical system disclosed in U.S. Pat. No. 3,674,334, and this mirror optical system separates the principal ray of an object light beam from an optical axis to thereby solve the above-noted problem of eclipse. The mirror optical system of FIG. 7 has, in the order of passage of the light beam, a concave mirror 131, a concave mirror 133, and they are originally reflecting mirrors rotation-symmetrical with respect to an optical axis 134, as indicated by dot-and-dash lines in FIG. 7. Of these mirrors, use is made of only the upper side of the concave mirror 131 relative to the optical axis 134 as viewed in the plane of the drawing sheet, only the lower side of the convex mirror 132 relative to the optical axis 134 as viewed in the plane of the drawing sheet, and only the lower side of the convex mirror 133 relative to the optical axis 134 as viewed in the plane of the drawing sheet to thereby construct an optical system in which the principal ray 136 of the object light beam 135 is separated from the optical axis 134. This eliminates the eclipse of the object light beam 135.
FIG. 8 of the accompanying drawings is a schematic view of the essential portions of a mirror optical system disclosed in U.S. Pat. No. 5,063,586. The mirror optical system of FIG. 8 solves the above-noted problem by making the central axis itself of a reflecting mirror eccentric relative to an optical axis and separating the principal ray of an object light beam from the optical axis.
When in FIG. 8, the vertical axis of an object surface 141 is defined as an optical axis 147, the central coordinates of the respective reflecting surfaces of a convex mirror 142, a concave mirror 143, a convex mirror 144 and a concave mirror 145 in the order of passage of the light beam and the central axes (axes passing through the centers of the reflecting surfaces and the centers of curvature of those surfaces) 142A, 143A, 144A and 145A are decentering or eccentric relative to the optical axis 147. In FIG. 8, the amount of eccentricity at this time and the radius of curvature of each surface are appropriately set to thereby prevent the eclipse of the object light beam 148 by each reflecting mirror, and efficiently form an object image on an imaging plane 146.
Besides the aforementioned patents, U.S. Pat. No. 4,737,021 and U.S. Pat. No. 4,265,510 disclose a construction in which use is made of a part of a reflecting mirror rotation-symmetrical with respect to an optical axis to avoid eclipse, or a construction in which the central axis itself of a reflecting mirror is made eccentric relative to an optical axis to thereby avoid eclipse.
Now, as a catadioptric optical system using both of a reflecting mirror and a refracting lens and having a focal length changing function, there are, for example, the deep sky telescopes of U.S. Pat. No. 4,477,456 and U.S. Pat. No. 4,571,036. These use a parabolic reflecting mirror as a main mirror and use an Elfre eyepiece mirror to make the magnification variable.
Also, there is known the zooming technique of moving the plurality of reflecting surfaces constituting the above-described mirror optical system relative to one another to thereby vary the imaging magnification (focal length) of the photo-taking optical system. For example, in U.S. Pat. No. 4,812,030, in the construction of the Cassegrainian reflector shown in FIG. 6, there is disclosed the technique of varying the spacing from the concave mirror 121 to the convex mirror 122 and the spacing from the convex mirror 122 to the image plane 123 relative to each other to thereby effect the focal length change of the photo-taking optical system.
FIG. 9 of the accompanying drawings shows another embodiment disclosed in the same publication. In FIG. 9, an object light beam 158 from an object impinges on a first concave mirror 151 and is reflected by the surface thereof and becomes a convergent light beam and travels toward the object side. The convergent light beam impinges on a first convex mirror 152, by which it is reflected toward the imaging plane side and becomes a substantially parallel light beam (and parallel to the optical axis 159) and impinges on a second convex mirror 154, and is reflected by the surface thereof and becomes a divergent light beam impinges on a second concave mirror 155, by which it is reflected and becomes a convergent light beam and is imaged on an image plane 157. In this construction, the spacing 153 between the first concave mirror 151 and the first convex mirror 152 is varied and also the spacing 156 between the second convex mirror 154 and the second concave mirror 155 is varied to thereby effect zooming and vary the focal length of the entire mirror optical system.
Also, in U.S. Pat. No. 4,993,818, the image formed by the Cassegrainian reflector shown in FIG. 6 is secondarily formed by another mirror optical system provided at the subsequent stage, and the imaging magnification of this mirror optical system for secondary imaging is varied to thereby effect the focal length change of the entire photo-taking system.
These photo-taking optical systems of the reflection type have many required constituents, and to obtain the necessary optical performance, it has been necessary to assemble respective optical parts with good accuracy. Particularly, the accuracy of the quickly retracted positions of the reflecting mirrors is severe and therefore, the adjustment of the position and angle of each reflecting mirror has been requisite.
As a method of solving this problem, there has been proposed a method of making, for example, the mirror system into a block to thereby avoid the incorporation errors of the optical parts caused during the assembly thereof.
As prisms in which a number of reflecting surfaces are made into a block, there have heretofore been optical prisms such as a pentagonal roof prism, an optical prism such as a porro prism used in the finder system of a camera, and a color resolving prism for resolving a light beam from a photo-taking lens into three color lights, e.g., red, green and blue lights, and imaging object images based on the respective color lights on the surfaces of corresponding image pickup elements.
These prisms have a plurality of reflecting surfaces molded integrally with one another and therefore, the relative positional relation among the reflecting surfaces is made accurately and the positional adjustment among the reflecting surfaces becomes unnecessary. However, the main function of these prisms is to change the direction of travel of rays of light to thereby effect the reversal of an image, and each reflecting surface is formed by a flat surface.
In contrast, there is also known an optical system in which the reflecting surface of a prism is given a curvature.
FIG. 10 of the accompanying drawings is a schematic view of the essential portions of an observation optical system disclosed in U.S. Pat. No. 4,775,217. This observation optical system is an optical system through which an outside scene is observed and also a display image displayed on an information displaying member is observed in overlapping relationship with the scene.
In this observation optical system, a display light beam 165 emitted from a display image on the information displaying member 161 is reflected by a surface 162 and travels toward the object side, and impinges on a half mirror surface 163 comprising a concave surface. The light beam is reflected by this half mirror surface 163, whereafter the display light beam 165 is made into a substantially parallel light beam by the refractive power of the concave surface 163, and is refracted by and transmitted through the surface 162, whereafter it forms the enlarged virtual image of the display image and also enters an observer""s pupil 164 to thereby make the observer recognize the display image.
On the other hand, an object light beam 166 from an object enters a surface 167 substantially parallel to the reflecting surface 162, and is refracted thereby and passes to the concave half mirror surface 163. Semi-transmitting film is deposited by evaporation on the concave surface 163, and a part of the object light beam 166 is transmitted through the concave surface 163, and is refracted by and transmitted through the surface 162, whereafter it enters the observer""s pupil 164. Thereby, the observer visually confirms the display image in overlapping relationship with the outside scene.
FIG. 11 of the accompanying drawings is a schematic view of the essential portions of an observation optical system disclosed in Japanese Patent Application Laid-Open No. 2-297516. This observation optical system also is an optical system through which an outside scene is observed and a display image displayed on an information displaying member is observed in overlapping relationship with the scene.
In this observation optical system, a display light beam 174 emitted from the information displaying member 170 is transmitted through a flat surface 177 constituting a prism Pa and enters the prism Pa and impinges on a parabolic reflecting surface 171. The display light beam 174 is reflected by this reflecting surface 171 and becomes a convergent light beam and is imaged on a focal plane 176. At this time, the display light beam 174 reflected by the reflecting surface 171 has arrived at the focal plane 176 while being totally reflected between two parallel flat surfaces 177 and 178 constituting the prism Pa, whereby the thinning of the entire optical system is achieved.
The display light beam 174 emerging as a divergent light from the focal plane 176 then enters a half mirror 172 comprising a parabolic surface while being totally reflected between the flat surface 177 and the flat surface 178. Light beam 174 is reflected by half mirror surface 172 and at the same time, forms the enlarged virtual image of the display image by the refractive power thereof and becomes a substantially parallel light beam. Then, light beam 174 is transmitted through the surface 177 and enters an observer""s pupil 173 to thereby make the observer recognize the display image.
On the other hand, an object light beam 175 from the outside is transmitted through a surface 178b constituting a prism Pb, and is transmitted through the half mirror 172 comprising a parabolic surface, and is transmitted through the surface 177 and enters the observer""s pupil 173. The observer visually confirms the display image in overlapping relationship with the outside scene.
Further, optical heads for light pickup using an optical element having a surface of a prism made into a reflecting surface are disclosed, for example, in Japanese Patent Application Laid-Open No. 5-12704 and Japanese Patent Application Laid-Open No. 6-139612. These reflect a light from a semiconductor laser by a Fresnel surface or a hologram surface, and thereafter image it on a disc surface, and direct the reflected light from the disc to a detector.
Here, in any of the mirror optical systems having an eccentric mirror which are disclosed in the aforementioned U.S. Pat. No. 3,674,334, U.S. Pat. No. 5,063,586 and U.S. Pat. No. 4,265,510, each reflecting mirror is disposed with a different amount of eccentricity and the mounting structure for each reflecting mirror is very cumbersome and it is very difficult to secure mounting accuracy.
Also, in any of the photographing optical systems having the focal length changing function which are disclosed in U.S. Pat. No. 4,812,030 and U.S. Pat. No. 4,993,818, the number of constituent parts such as reflecting mirrors and an imaging lens is great, and to obtain necessary optical performance, it has been necessary to assemble the respective optical parts with good accuracy.
Also, particularly the accuracy of the relative position of the reflecting mirrors becomes severe and, therefore, it has been necessary to effect the adjustment of the position and angle of each reflecting mirror.
Also, the photographing optical system of the reflection type according to the prior art is of a construction suitable for a lens system of the so-called telephoto type in which the full length of the optical system is great and the angle of view is small. To provide a photographing optical system which requires the angle of view of a standard lens to the angle of view of a wide angle lens, the number of reflecting surfaces required in aberration correction becomes great and therefore, higher accuracy of parts and higher accuracy of assembly become necessary. This has led to a tendency toward a higher cost or the bulkiness of the whole system.
Also, the observation optical systems disclosed in the aforementioned U.S. Pat. No. 4,775,217 and Japanese Patent Application Laid-Open No. 2-297516 aim principally at the pupil imaging action for efficiently transmitting to the observer""s pupil the display image displayed on the information displaying member disposed separately from the observer""s pupil, and changing the direction of travel of rays of light. These publications do not directly disclose the technique of effecting positive aberration correction by a reflecting surface having a curvature. Also, the optical systems for light pickup disclosed in Japanese Patent Application Laid-Open No. 5-12704 and Japanese Patent Application Laid-Open No. 6-139612 are both restricted to the use of a detecting optical system, and have not satisfied the imaging performance for a photographing optical system, particularly an image pickup device using an image pickup element of the area type such as a CCD.
In contrast, the applicant of the basic application filed in Japan discloses in Japanese Patent Application Laid-Open No. 8-292371 describes an optical element in which a refracting surface on which a light beam is incident, a plurality of reflecting surfaces each having a curvature, and a refracting surface from which light beams reflected by these reflecting surfaces emerge are integrally molded on the surface of a transparent member, and an optical system using the same.
By using such an optical element, there is provided an optical system in which the compactness of an entire mirror optical system is achieved and yet the disposition accuracy (assembly accuracy) of a reflecting mirror liable to be in the mirror optical system is relaxed. Also, by adopting a construction in which a stop is disposed most adjacent to the object side of an optical system and an object image is formed at least once in the optical system, the shortening of the effective diameter of the optical system is achieved inspite of being an optical system having a wide angle of view. Appropriate refractive power is given to a plurality of reflecting surfaces constituting optical elements, and a reflecting surface constituting each optical element is eccentrically disposed to thereby provide an optical system in which the optical path is bent into a desired shape and of which the full length in a predetermined direction is shortened.
In the optical element proposed in the aforementioned Japanese Patent Application Laid-Open No. 8-292371, a method of holding other optical part such as an optical filter than an imaging optical system has not been particularly referred to.
It is an object of the present invention to provide an optical unit in which an incidence surface on which a light beam is refracted and incident, a plurality of reflecting surfaces each having a curvature for successively reflecting the incident light beam, and an emergence surface from which the light beam reflected by the plurality of reflecting surfaces is refracted and emerge are integrally formed on the surface of a transparent member, wherein an optical member such as an optical filter is adhesively secured to the incidence surface and/or the emergence surface, whereby any special holding member for the optical member is made unnecessary and the simplification of the entire device is achieved, and an optical system using the same.
It is also an object of the present invention to provide an optical system in which a solid state image pickup element is adhesively secured to the optical unit to thereby effect the positioning of the two, and any positional deviation after the manufacture of the optical system is prevented.
It is also an object of the present invention to provide an optical unit in which the area of contact of the optical effective portion of the optical member or the solid state image pickup element with the atmosphere is decreased to thereby reduce the influence of dust, and an optical system using the same.
The optical unit of the present invention is characterized in that an incidence surface on which a light beam is incident, a plurality of reflecting surfaces each having a curvature for successively reflecting the light beam from the incidence surface, and an emergence surface from which the light beam reflected by the plurality of reflecting surfaces emerges are integrally formed on the surface of a transparent member, and a light transmitting member is fixed near said the incidence surface and/or the emergence surface.
The optical unit of the present invention is particularly characterized in that
the light transmitting member is adhesively fixed,
another light transmitting member is adhesively fixed to the light transmitting member,
the light transmitting member is adhesively fixed to the flat portion of the incidence surface and/or the emergence surface,
the light transmitting member is an optical lowpass filter or an infrared cut filter,
the another light transmitting member is cover glass covering the image pickup surface of the solid state image pickup element, and
the light transmitting member is a prism having a reflecting surface.
The optical system of the present invention is characterized by at least one optical unit of the above-described construction.